This invention relates to a process and a device for producing a composite thread, formed by the association of a multiplicity of continuous glass filaments and of continuous filaments of thermoplastic organic material. The production of such a composite thread is described for example in U.S. Pat. No. 5,011,523. The '523 patent describes installations comprising a die, from which are drawn continuous filaments of glass, and a drawing head, supplied under pressure with a thermoplastic organic material, for delivering continuous organic filaments. The two types of filaments may be in the form of sheets, or of sheet and thread, during their assembling together. One advantageous form of embodiment described in the '523 patent consists of surrounding the filaments or thread of glass with organic filaments as they are combined together. A composite thread formed in this manner has the advantage of protecting the glass filaments from friction against the solid surfaces with which the composite thread comes into contact. On the other hand, this arrangement does not favor perfect homogenization of the mixture of the two types of filaments. In fact, a cross-section through the composite thread shows preferential zones for each type of filament, which may be a desired method of assembly for certain applications.
Furthermore, these composite threads possess an undulation. This is very evident when the threads are present in the form of spools, because the spools exhibit undulations around their entire periphery. This undulation of the composite thread is, in fact, due to a shrinkage phenomenon of the organic filaments within a composite thread which causes an undulation of the glass filaments. This phenomenon has various disadvantages. In the first place, it requires thick core tubes for making the spools, so that they shall withstand the binding effect exerted by the composite thread. Moreover, the unwinding from the spool becomes very difficult by reason of the changes in geometry. This form of presentation of the thread may be advantageous where, for example, it forms part of the structure of a fabric which will later serve for reinforcing a curved component. The flexibility of the fabric, imparted to it both by the aptitude for deformation of the organic filaments and the undulation of the glass filaments, makes it easier to position in a mould. In contrast, for the production of composite threads intended for the manufacture of plane components reinforced in one direction, this presentation is a handicap. Since the filaments are not aligned in the final composite, their reinforcing capability in one specific direction is reduced.